Protein T1, T2 and T1 rho of water in muscle and other body tissues (brain, kidney, and liver) of mice in different stages of their aging process will be studied. Care will be taken to quantitatively determine the amounts of organic protons (by pulse nuclear magnetic resonance), extracellular water (by centrifugation), and non-freezable water (by differential scarring calorimetry, DSC) in each sample. The proton resonance work will be done at different temperatures and frequencies. For 23Na resonance, T, T1 rho and self-diffusion coefficient (D) of Na ion in various tissues of mice will be studied as a function of temperature. Heat capacity of hydrated collagen fibers and non-freezable water in body tissues will be studied by DSC. The adsorption of adenosine triphosphate (ATP) on collagen fibers will be studied by UV spectroscopy. The effects of ATP concentration, pH, and cross-linking will be investigated.